Cancer is a term used for diseases in which abnormal cells divide without control and are able to invade other tissues.Cancer harms the body when damaged cells divide uncontrollably to form lumps or masses of tissue called tumors .

A growing tumor becomes a lump of cancer cells that can destroy the normal cells around the tumor and damage the body's healthy tissues.Tumors that stay in one spot and demonstrate limited growth are generally considered to be benign.Cancer cells can spread to other parts of the body through the blood and lymph systems.

In case of leukemia cancer prohibits normal blood function by abnormal cell division in the blood stream.
When a tumor successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a serious condition that is very difficult to treat.There are more than 100 different types of cancer. Most cancers are named for the organ or type of cell in which they start for example the cancer in basal cells of the skin is called basal cell carcinoma.